Dear Sumera Sumera,

you might try also a full text search within either publications (as stored in RG-archives) or in the Q/A-archives of RG (find the SEARCH function upper menu bar, SEARCH, click into downpointing arrow and find pull down menu: - in Publications, in Questions)....etc. for the latter, e.g. searching "only" for | LAEMMLI buffer | creates a LINK in your browser: https://www.researchgate.net/search.Search.html?type=question&query=Laemmli+buffer and after some second will display a lot of Q/A-threads you might find interesting to read.

(one of them might give you adequate answers: https://www.researchgate.net/post/Does_it_matter_to_freshly_add_reducing_agent_DTT_or_bME_to_Laemmli_sample_buffer_before_boiling_Does_not-fresh_add_give_the_same_result_in_WB : shelf life for months at -20°C).

Laemmli buffer supposed to be composed of:

65mM Tris-HCl, 10% glycerol, 2% SDS, 0.025% bromophenol blue.

From that "ingredients" I suppose shelflife of the solution @ RT (given that the transfer of clean solution into clean glass ware and under proper storage conditions) to be at least 2-3 days (or perhaps even longer).

PS: PLEASE, find the EDIT function (downpointing arrowhead @ right upper edge of your Question-form- click into and find "EDIT"), CORRECT "laemilli" inserting 'LAEMMLI' and click SAVE ANSWER again to activate your corrected Q-text.